Biomedical subjects

C Ioannides

Publications and source records attributed to C Ioannides.

At least 181 records · Page 10Linked to original sources

PubMed1987

Spectral and kinetic studies of the interaction of imidazole anti-fungal agents with microsomal cytochromes P-450.

1. The imidazole antifungal agents, ketoconazole, miconazole and clotrimazole have been shown to be potent inhibitors of the phenobarbital-induced cytochromes P-450 and the 3-methylcholanthrene-induced cytochromes P-448-dependent rat hepatic microsomal mixed-function oxidases. 2. All three drugs were more potent inhibitors of the phenobarbital-induced O-deethylation of ethoxycoumarin than of the 3-methylcholanthrene-induced activity indicating selective inhibition of the phenobarbital-induced cytochromes P-450. In both types of microsomes ketoconazole was always the weakest inhibitor. 3. All three compounds elicited type II spectral interactions with both types of microsomes, and had similar Ks values. Miconazole and clotrimazole, and to a lesser extent ketoconazole, also interacted with the substrate binding sites of both phenobarbital-induced cytochromes P-450 and to a lesser extent with the 3-methylcholanthrene-induced cytochrome P-448. 4. It is concluded that at least part of the inhibitory effect of these antifungal agents may reflect competitive inhibition at the substrate binding site.

Animals↗

PubMed1986

Induction of cytochrome P-448 activity as exemplified by the O-deethylation of ethoxyresorufin. Effects of dose, sex, tissue and animal species.

The effects of tissue, sex, animal species and dose on the induction of cytochrome P-448 activity by various inducing agents were investigated using O-ethoxyresorufin as a model substrate. The liver was by far more effective in catalysing the O-deethylation of ethoxyresorufin (EROD) than the lung and kidney. The extent of induction was also highest in the liver, with the exception of benzo(a)pyrene and 3-methylcholanthrene where inducibility was more pronounced in the kidney. The benzo(a)pyrene-induced hepatic EROD activity in the rat decayed to reach control levels four days after a single administration. Rat hepatic EROD activity was induced in both sexes but tended to be higher in the male. Marked species differences in the inducibility of hepatic EROD activity by various chemicals was observed, the rat being always more responsive when compared to the hamster or mouse. The induction of rat hepatic EROD activity by benzo(a)pyrene, 2-acetylaminofluorene and safrole was dose-dependent, maximum induction being achieved with single doses of 5, 2 and 5 mg/kg, respectively.

Animals↗

PubMed1986

Molecular dimensions of the substrate binding site of cytochrome P-448.

The molecular geometries of specific substrates, inhibitors and inducers of cytochrome P-448 activity were determined using computer-graphic techniques for use in defining the molecular dimensions of the substrate binding site of this enzyme. Specific substrates of cytochrome P-448 are essentially planar molecules characterised by a small depth and a large area/depth ratio. In contrast, compounds that do not serve as substrates of cytochrome P-448 are bulky, non-planar molecules characterised by small area/depth ratios and greater flexibility in molecular conformation. Specific inhibitors of cytochrome P-448 whose effect is mediated through interaction with the haem still meet the dimensional criteria for substrates indicating that they must also interact with the substrate binding-site, which is probably located in proximity to the haem. Inducers of cytochrome P-448 activity exhibit similar molecular geometries to the substrates from which it may be inferred that the cytosolic receptor associated with the induction of cytochrome P-448 activity is structurally related to the active site of the cytochrome.

Animals↗

PubMed1986

Induction of rat hepatic mixed function oxidases by aromatic amines and its relationship to their bioactivation to mutagens.

Hepatic microsomal mixed-function oxidase activities were determined in rats pretreated with the aromatic amines 2-aminoanthracene, 2-naphthylamine or 4-aminobiphenyl. All three amines stimulated the O-deethylation of ethoxyresorufin (cytochromes P-448) but none had any effect on the p-hydroxylation of aniline. 2-Aminoanthracene and 4-aminobiphenyl also stimulated the NADPH-dependent reduction of cytochrome c and 2-naphthylamine inhibited the N-demethylation of benzphetamine. Hepatic preparations from animals pretreated with 2-aminoanthracene were more efficient in converting this carcinogen to mutagens while in contrast pretreatment with Aroclor 1254 caused a marked decrease in mutagenicity. 4-Aminobiphenyl also enhanced its own activation but Aroclor-pretreated preparations were the most effective. The latter preparations were also more efficient than controls in activating 2-naphthylamine to mutagens. It is concluded that 4-aminobiphenyl and 2-aminoanthracene enhance their own activation at least partly, by inducing the synthesis of cytochromes P-448.

2-Naphthylamine↗

PubMed1986

Alkoxyresorufin O-dealkylases: association with the murine Ah locus.

The hepatic microsomal dealkylation of a series of alkoxyresorufins and the oxidation of phenoxazone to resorufin were investigated in C57BL/6 and DBA/2 mice of both sexes. In both strains of mice and in both sexes the dealkylation rate decreased with increasing length of the alkyl chain. With all alkoxyresorufins the dealkylation rates were higher in the C57BL mice than the DBA mice, whereas the rate of phenoxazone hydroxylation was higher in the latter. In the C57BL mice, and to a lesser extent in the DBA mice, females were more efficient in dealkylating the resorufin ethers. Treatment with 3-methylcholanthrene (3MC) enhanced the rates of dealkylation of all alkoxyresorufins in the C57BL mice but not in the DBA mice, the extent of stimulation being highest for the propoxy- and butoxyresorufins and least for pentoxy-, heptoxy- and benzyloxyresorufins. The same treatment had no effect on the oxidation of phenoxazone in either strain of mice. It is concluded that the dealkylation of alkoxyresorufins, not the oxidation of phenoxazone, is associated with the murine Ah locus.

Animals↗

PubMed1986

Hepatic microsomal mixed-function oxidase activity in ethanol-treated hamsters and its consequences on the bioactivation of aromatic amines to mutagens.

Male golden Syrian hamsters were maintained on ethanol-containing liquid diets for 4 weeks, corresponding to an average daily intake of 17 g/kg body wt. The p-hydroxylation of aniline was markedly enhanced by this treatment while minimal effects were seen in benzphetamine N-demethylase and ethoxyresorufin O-deethylase activities; there was no change in the microsomal levels of cytochromes P-450. Hepatic microsomal preparations from the ethanol-treated hamsters were more efficient than controls fed isocaloric diets in converting 2-aminofluorene, 4-aminobiphenyl, benzidine and 2-acetylaminofluorene into mutagens in the Salmonella mutagenicity test. The same treatment had no effect on the metabolic activation of 2-naphthylamine and even inhibited the mutagenicity of 2-aminoanthracene. No increase was seen in the activation of the two polycyclic aromatic hydrocarbons, benzo[a]pyrene and 3-methylcholanthrene to mutagens and an inhibitory effect was seen with the former. The ethanol-induced increase in the mutagenicity of 2-aminofluorene was inhibited by 2-butanol but not by the hydroxyl radical scavenger dimethylsulphoxide. It is concluded that chronic ethanol ingestion modulates the bioactivation of aromatic amines and amides to mutagens, the effect being substrate dependent. This effect of ethanol may be catalysed by unique form(s) of cytochrome P-450 whose synthesis is induced by such treatment.

Amines↗

PubMed1986

Differential effects of chronic alcohol administration to rats on the activation of aromatic amines to mutagens in the Ames test.

Male Wistar albino rats were maintained on alcohol-containing liquid diets for 4 weeks. Hepatic post-mitochondrial preparations derived from these animals were more efficient than control in activating 4-aminobiphenyl and 2-aminofluorene to mutagens in the Ames test. The alcohol-induced enhancement in mutagenicity was not inhibited by dimethylsulphoxide indicating that the generation of hydroxyl radicals is not involved. The activation of 2-naphthylamine was not affected by the treatment with alcohol but the mutagenicities of 2-aminoanthracene, benzo[a]pyrene and 3-methylcholanthrene were inhibited. The same treatment markedly increased hepatic microsomal aniline p-hydroxylase and ethoxyresorufin O-de-ethylase activities and to a lesser extent benzphetamine N-demethylase and microsomal levels of total cytochromes P-450. It is concluded that chronic alcohol administration to rats modulates the metabolic activation of pre-carcinogens to their reactive intermediates presumably by causing the redistribution of cytochrome P-450 isozymes.

Amines↗

PubMed1986

Metabolic activation of 2-amino-3-methylimidazo(4,5-f)quinoline by hepatic preparations--contribution of the cytosolic fraction and its significance to strain differences.

In accordance with previous studies the bioactivation of 2-amino-3-methylimidazo(4,5-f)quinoline (IQ) to mutagens in the Ames test was preferentially catalysed by the 3-methyl-cholanthrene-induced cytochromes P-448, in contrast to the phenobarbital-induced forms of the cytochrome. The mutagenicity of IQ catalysed by microsomes, in the absence of cytosol, was much lower when compared with that observed with S9 fractions. Cytosol itself could not activate IQ but markedly potentiated the microsome-mediated mutagenicity of the carcinogen. The effect of the cytosol was still evident when microsomal metabolism was terminated, indicating that the cytosol contains enzyme(s) that can further convert the microsome-generated metabolites of IQ to more potent mutagens. The cytosolic enzyme(s) were inducible by pre-treatment of the rats with Aroclor 1254. The higher efficiency of activation of IQ to mutagens by Sprague-Dawley S9 mixes when compared with similar preparations from the Wistar rat could be attributed not only to differences in the rate of microsomal metabolism but also to the higher ability of the Sprague-Dawley cytosolic fraction in further metabolizing the microsome-generated metabolite(s). The present study demonstrates clearly that the mutagenic response of this compound in the Ames test may be profoundly modulated by the cytosolic fraction and its role in the metabolic activation of pre-mutagens merits further investigation.

Animals↗

PubMed1986

Effects of brotizolam on mixed-function oxidases and glutathione metabolism in the rat.

Intra-gastric administration of brotizolam (0.1-200 mg/kg) daily for three days to rats resulted in no significant changes in the hepatic and intestinal cytochrome P-450-dependent or P-448-dependent mixed-function oxidases, or in the hepatic flavoprotein dimethylaniline N-oxidase. Liver microsomes from mouse, rat and man metabolized brotizolam by hydroxylation of the diazepine ring and of the methyl group at rates which were greater for mouse greater than rat greater than man. Brotizolam and its metabolites generated by rat-liver microsomes in vitro were not mutagenic in the Ames' test. Brotizolam, at 200 mg/kg per day for two to six weeks, depleted liver glutathione concentration and markedly increased liver gamma-glutamyl transpeptidase, glutathione reductase and glutathione transferase activities. Similar changes were not seen at the lower dose of 0.3 mg/kg. The observed increases in glutathione metabolism and the decreased tissue concentration of glutathione are indicative of high levels of glutathione conjugation, and provide a possible explanation for the equivocal increase in tumorigenicity seen in rats receiving brotizolam at high dosage.

Animals↗

PubMed1985

Foetal and neonatal development of cytochrome P-450 and cytochrome P-448 catalysed mixed function oxidases in the rat: induction by 3-methylcholanthrene.

Benzphetamine N-demethylase (cytochrome P-450) and ethoxyresorufin O-deethylase activities (cytochrome P-448) were determined in the growing neonate and foetus of control and 3-methylcholanthrene-pretreated rats. Ethoxyresorufin O-deethylase activity was highest in the 1-2-week-old animals and then decreased with age. The inducibility of this activity by 3-methylcholanthrene was low in the young animals, but increased with age. In contrast, benzphetamine N-demethylase activity in the control animals was low at birth and increased with age, and was not induced by 3-methylcholanthrene. In the foetal liver, ethoxyresorufin O-deethylase was the only activity present at higher levels than in the maternal liver. Transplacental administration of 3-methylcholanthrene failed to induce the foetal activities while the maternal liver showed the expected response. These observations demonstrate that cytochrome P-448 may be a predominant hepatic form in the foetus and neonate but cytochrome P-450 becomes a major form as the animal grows. The implications of these findings in chemical toxicity are discussed.

Age Factors↗

PubMed1985

Mechanism of the protective action of n-acetylcysteine and methionine against paracetamol toxicity in the hamster.

The mechanism of the protective action of methionine and N-acetylcysteine against the toxicity of paracetamol was investigated in vivo. N-acetylcysteine inhibited the O-deethylation of ethoxyresorufin (cytochrome P-448) while methionine enhanced the N-demethylation of benzphetamine (cytochrome P-450) and increased hepatic microsomal levels of cytochrome P-450. These observations indicate that N-acetylcysteine, but not methionine, could afford protection against paracetamol hepatotoxicity, at least partly, by inhibiting cytochrome P-448 activity and thus the generation of the reactive intermediate. However, previous studies demonstrating no decrease in the urinary excretion of glutathione conjugates of paracetamol (derived from the reactive intermediate) in animals treated with N-acetylcysteine suggest that this is unlikely to be the prevailing mechanism of action. Administration of a large dose of paracetamol, as expected, depleted glutathione levels and inhibited cytosolic glutathione transferase activity. Administration of either N-acetylcysteine or methionine 1 h after paracetamol prevented both effects. On the basis of the present work and previously published observations, it is concluded that the major mechanism of action of N-acetylcysteine and methionine in vivo is by acting as precursors of intracellular glutathione.

Acetaminophen↗

PubMed1985

The homogeneity of rat liver microsomal cytochrome P-448 activity and its role in the activation of benzo[a]pyrene to mutagens.

The O-deethylation of ethoxyresorufin and the metabolic activation of benzo[a]pyrene to mutagens were determined in hepatic microsomal preparations from control and induced animals. An excellent direct correlation (r = 0.95) has been observed between ethoxyresorufin O-deethylase and the metabolic activation of benzo[a]pyrene to mutagens when the fraction of cytochromes P-450 present as cytochrome P-448 was altered by the administration of phenobarbitone and 3-methylcholanthrene alone or in combination with 9-hydroxyellipticine. The correlation between these activities was maintained following treatment of animals with Arochlor 1254, benzo[a]pyrene, benzo[e]pyrene, 7,12-dimethylbenzo[a]anthracene,2-anthramine and 2-naphthylamine.

Animals↗

PubMed1985

The modulation by arylamines of the in vitro formation of superoxide anion radicals and hydrogen peroxide by rat liver microsomes.

A concentration-dependent increase in the generation of the superoxide anion radical (O-2), was observed during the incubation of benzidine (0.1-5 mM), but not of the structurally related compounds 4-aminobiphenyl, 2-aminobiphenyl or 4-fluoro-4'-aminobiphenyl, with NADPH-supplemented rat liver microsomes. This increase was partially inhibited by carbon monoxide and catalase but unaffected by 4-aminobiphenyl, a substrate of the cytochrome P-450 system. Microsomes from benzo(a)pyrene-treated, but not microsomes from phenobarbitone-pretreated rats, were responsible for a larger benzidine-dependent effect compared to microsomes from control animals. In contrast to the above observations, benzidine decreased the formation of hydrogen peroxide by NADPH-supplemented microsomal preparations from untreated rats. These results indicate that free radicals of oxygen are generated during the metabolism of some arylamines.

Amines↗

PubMed1985

Interactions of safrole and isosafrole and their metabolites with cytochromes P-450.

The structural features which determine interaction of safrole and related methylenedioxyphenyl compounds with cytochromes P-450 or P-448, and determine the induction of these two classes of the cytochrome, have been studied. All methylenedioxyphenyl compounds studied interact with both cytochromes P-450 and P-448 eliciting type I spectral changes and it has been found that the allyl 4-substituent is important in these interactions. Methylenedioxyphenyl compounds with an oxidised allyl 4-substituent exhibited higher affinity for cytochrome P-448 while those possessing an intact allyl or methylvinyl group generally showed higher affinity for cytochrome P-450. Compounds possessing intact allyl and methylenedioxyphenyl groups (safrole, isosafrole and myristicine) were the most potent inducers of cytochromes P-450 and P-448; compounds containing an intact allyl group only (estragole, allybenzene and eugenol methyl ether) or an oxidized allyl group and an intact methylenedioxyphenyl group (epoxysafrole) were inducers of P-448 only.

Animals↗

PubMed1985

Perforation of the intra-articular disc diagnosed by arthro-tomography of the temporomandibular joint.

Arthrography was first used almost 40 years ago for evaluation of the non-osseous parts of the TMJ. It did not find wide application and only during the last decade have certain authors re-introduced its use as a diagnostic approach in TMJ pathology. Among the other pathological conditions which can be diagnosed, is a perforation of the intra-articular disc. Four such cases are presented and the value of this method is shown.

Adult↗

PubMed1985

Ligand-complex formation between cytochromes P-450 and P-448 and methylenedioxyphenyl compounds.

The formation of ligand complexes between hepatic microsomal cytochrome P-450 and safrole, isosafrole and other methylenedioxyphenyl compounds was studied in vivo and in vitro in rats pretreated with either phenobarbital or 3-methylcholanthrene. Both the phenobarbital-induced cytochrome P-450 and the 3-methylcholanthrene-induced cytochrome P-448 metabolically convert safrole, isosafrole, and those metabolites possessing an intact methylenedioxy group, to reactive metabolites which then interact with the cytochromes to form ligand complexes. Formation of these ligand complexes was accompanied by loss of mixed-function oxidase activities, and dissociation of the complexes with the type I substrate biphenyl restored activities. Safrole and, to a lesser extent, 1'-hydroxysafrole formed complexes in vivo when administered to phenobarbital-pretreated rats; none was obtained with epoxysafrole. However, when administered to 3-methylcholanthrene-pretreated animals all three compounds formed complexes, safrole being the least effective. Epoxysafrole and 1'-hydroxysafrole administered to phenobarbital-pretreated rats resulted in slight inhibition of the type I binding of safrole to liver microsomal P-450 in vitro; in contrast, with 3-methylcholanthrene-pretreated animals marked competitive inhibition was observed. This study shows that oxidation of the allyl chain of safrole analogues enhances their affinity for cytochrome P-448, but not for cytochrome P-450, and further demonstrates that these cytochromes possess distinctly different binding sites.

Animals↗

PubMed1985

Inhibition of the mutagenicity of aromatic amines by the plant flavonoid (+)-catechin.

Addition of the plant phenolic flavonoid (+)-catechin to rat liver microsomes inhibited the mutagenicity of the aromatic amines 2-aminofluorene and 4-aminobiphenyl in the Ames test. Similarly, (+)-catechin decreased the mutagenicity of N-hydroxy-4-amino-biphenyl, the proximate carcinogen, but, in contrast, had no effect on the mutagenicity of other direct-acting carcinogens such as N-methyl-N'-nitro-N-nitrosoguanidine and 9-aminoacridine. In vitro addition of (+)-catechin gave rise to a dose-dependent inhibition of the cytochrome P-450-dependent benzphetamine N-demethylase and ethoxyresorufin O-deethylase activities. This was achieved by impairment of the electron flow from the reduced pyridine nucleotide to the cytochrome. However, administration of (+)-catechin to rats had no effect on the in vitro mixed-function oxidase activities. It is concluded that the (+)-catechin inhibits the mutagenicity of aromatic amines in the Ames test by interfering with their cytochrome P-450-dependent bioactivation and by direct interaction with the proximate carcinogen, but the former mechanism is unlikely to occur in vivo because the high doses of the flavonoid required are not achieved.

Amines↗

PubMed1984

Determination of cytochrome P-448 activity in biological tissues.

Three enzymes used for the determination of cytochrome P-448 activity, namely aryl hydrocarbon hydroxylase, biphenyl 2-hydroxylase and ethoxyresorufin O-de-ethylase, were evaluated with respect to their specificity, sensitivity and inducibility. Purified cytochrome P-448 (LM4), but not cytochrome P-450 (LM2), catalysed the O-de-ethylation of ethoxyresorufin in a reaction that was markedly inhibited by 9-hydroxyellipticine. After the administration of 3-methylcholanthrene to rats all three activities were induced, the extent of induction being highest for ethoxyresorufin O-de-ethylase. Administration of very small doses of benzo[a]pyrene (50 micrograms/kg) to rats to induce cytochrome P-448 specifically increased only the O-de-ethylation of ethoxyresorufin. 3-Hydroxybenzo[a]pyrene, the major metabolite determined by the aryl hydrocarbon hydroxylase assay, undergoes further NADPH-dependent oxygenation leading to loss of fluorescence. On the basis of these observations and those by other workers, we conclude that ethoxyresorufin O-de-ethylase provides the most specific, sensitive and reproducible means of determining cytochrome P-448 activity.

Animals↗